The present invention relates generally to the field of electrical neuromuscular stimulation for the treatment of urinary incontinence in women. In particular, the present invention is a molded vaginal electrode having increased effectiveness, an improved method of construction and increased safety.
Electrical neuromuscular stimulation is widely used to assist persons afflicted with motor dysfunctions in performing muscle contraction maneuvers. Motor nerve fibers are electrically stimulated by means of transcutaneously applied pulses of electrical current to cause contraction of the innervated muscles. This technique is also used to re-educate patients in the proper use of the dysfunctional muscles.
For example, in cases in which urinary incontinence in women is caused by the patient's inability to properly contract the external sphincter of the urethra, it has been shown that neuromuscular stimulation of the dysfunctional muscles by means of a vaginal or anal electrode can effectively prevent the unwanted flow of urine. Through the use of such an electrode, some patients can educate themselves to voluntarily or automatically impede the flow of urine.
A more important application of the pelvic floor stimulation is the exercise and toning of the muscles of the pelvic floor which support the bladder, vagina, urethra and other organs. Muscles which have become lax or stretched through the processes of childbirth or natural aging, can be strengthened and tightened to properly support these structures, thus affecting positively the patient's ability to maintain continence. Another common form of incontinence in women is called urge incontinence. This condition results either from an irritable bladder or a hyperactive bladder muscle. Electrical stimulation can activate certain reflexes which inhibit the inappropriate bladder contractions ("urgency") associated with urge incontinence.
Electrical stimulators for controlling urinary incontinence generally include a relatively rigid vaginal plug with one or more electrodes in the form of conductive metal rings. A lead harness extends from the plug to a controller or stimulator which generates stimulation signals. The controller is usually worn externally, attached to the user's clothing.
Proper positioning of the electrode within the vagina is essential to deliver current to the motor nerve intended to be affected. Incorrect positioning may result in reduced efficiency of stimulation. Furthermore, the size, shape and weight of the electrode affect the retainability of the proper position of the electrode.
Vaginal electrodes which are relatively rigid cause compression of blood vessels which supply the contracting pelvic muscles, and compression of pressure sensors in the vaginal tissue during contraction. This results in an undesirable anaerobic and uncomfortable contraction.
The use of metal for the conductive bands of vaginal plugs also has some drawbacks. Metallic conductors of vaginal electrodes known in the art have an impedance substantially lower than that of vaginal tissue. When this type of impedance relationship exists, the current density tends to be greatest at the edge of the conductive ring. This "edge effect" can result in burns of the tissue in contact with the conductor if the current reaches a high enough intensity. The severity of the "edge effect" is proportional to the impedance differential between the conductor and the tissue with which it is in contact. Therefore, the use of such vaginal electrodes with metallic conductors can potentially cause pain, discomfort and injury to the patient.
Integrity problems generally plaque the coupling of the electrical leads to conductive polymers. Overmolding of tabs, rings or stripped wires during the molding process is a typical method of establishing contact. This connection method, however, has proved ineffective. Various factors can contribute to diminished contact integrity between the metal and conductive polymer thereby increasing the electrical impedance and decreasing the effectiveness of the electrode. These factors include heat-induced pull-away of the polymeric compounds from the metal contacts during the molding process, "stress creep" (elastomeric relaxation) of the polymeric compounds, flexing of the vaginal electrode due to contractions of the vaginal muscles, and corrosive attack of the surface of the metal by catalysts or other residuals in the polymer.
Vaginal electrodes known in the art deliver electrical signals to the vaginal musculature by means of a single channel. The limitation of providing a therapeutic signal at a single frequency band per therapy session theoretically compromises the effectiveness of treatment. Optimum treatment of stress incontinence has been shown to involve delivery of a frequency and amplitude of current different than the optimum frequency and current amplitude recommended for the treatment of urge incontinence.
There is a continuing need for lightweight, flexible vaginal electrodes which can prevent the unwanted flow of urine, and which can retrain the dysfunctional muscles responsible for stress and urge incontinence. In addition to being effective, the electrode must be durable, hygienical and inexpensive to manufacture.